Active knee bolsters have been developed to enhance vehicle occupant protection in the event of sudden vehicle decelerations. Active knee bolsters increase the duration of deceleration of an occupant's body and more particularly, the occupant's femurs. Further, the knee bolsters help to control a vehicle occupant's upper torso kinematics during a frontal impact event.
In operation, an impact surface of the active knee bolster is moved from a stored position to an extended position to intercept an occupant's knees, as early as possible, during a vehicle impact event. Consequently, the knees of an occupant are decelerated over a longer period of time. Thus, peak accelerations of the occupant's body, which may cause serious injury, are reduced. It is important that the knee bolster(s), in its retracted position or stored position, is compatible with vehicle styling as well as allows for easy ingress and egress of the vehicle occupants.
While known prior art active knee bolsters achieve their intended purpose, many problems still need to be addressed. For example, the differences in seat placement can affect the performance of knee bolsters. In fact, in certain seat positions, conventional active knee bolsters may not perform to a desired level and proper deployment of the active knee bolster may not take place leaving a vehicle occupant with less than optimal protection.
Current active knee bolsters and instrument panel structures closest to the driver and front passenger's knees are designed with the following crash safety objectives: 1) a controlled reaction force applied to the occupant's knees during contact with the knee bolster and 2) manage the resulting movement of the occupant, i.e., kinematics, during contact with the knee bolster. To accomplish this objective, the knee bolster is designed to crush in such a way so as to facilitate occupant ride down during the crash event. Knee bolster performance in a frontal crash is currently tailored for unbelted occupants and may be optimized for the fiftieth percentile male occupants, and thus, may not offer the same level of performance for the fifth percentile females or the ninety-fifth percentile males. The fifth percentile female occupant is smaller and lighter than the fiftieth percentile male occupant, and thus, develops much less energy in a crash event. Current knee bolsters systems are designed to provide favorable energy absorption, i.e., reaction, forces for the fiftieth percentile male occupants. But these systems may provide a static stiffness that is often too large to crush for the fifth percentile female occupant, thus providing a less than optimal reaction force for the lighter and smaller occupants.
Therefore, a new and improved system and method for enhancing occupant protection using an active knee bolster is needed. The new and improved knee bolster should be compatible with vehicle interior designs as well as not inhibit vehicle ingress and egress. Further, the performance of the actual knee bolster should not degrade with changes in seat position.